The present invention relates to a method of detecting an abnormal electric current in a vehicle, an apparatus for detecting an abnormal electric current in a vehicle, a power supply apparatus for a vehicle, and more particularly to preventing damage of an insulating coating for an electric wire for establishing the connection between a power source portion and each load.
Hitherto, a general structure for preventing damage of an electric wire has been formed in such a manner that a fuse arranged to be burnt before the electric wire is damaged is provided for a current input stage of the electric wire so that the fuse is burnt if an excess current passes which will damage the electric wire.
However, the above-mentioned structure having the fuse has a problem in that damage of the electric wire cannot reliably be prevented. If a dead short circuit takes place which causes great electric currents to continuously pass through an electric wire, the fuse is burnt so that damage of the electric wire is prevented. If an intermittent short circuit (a rare short circuit) or an inter-line short circuit takes place, pulse-shape excess currents continuously pass through the electric wire. In the foregoing state, heat is accumulated in the insulating coating for the electric wire while the fuse is not burnt, causing the temperature to be raised. Thus, the insulating coating is damaged because of the raised temperature.
The reason for this is that the fusing characteristic of the fuse is slow to react to the excess current pulses as compared with the damage characteristic of the electric wire. Therefore, a phenomenon occurs in which heat accumulation which takes place due to the excess current pulses causes only the temperature of the electric wire to be raised. As a result, damage of the insulating coating occurs. If a fuse is selected which is able to protect the electric wire from being damaged even with the pulse-shape excess currents, the above-mentioned problem can be prevented. However, a fuse adaptable to the damage characteristic of the electric wire which varies in accordance with the type and length of the electric wire cannot easily be selected for each electric wire.
If an electric wire encounters an intermittent short circuit, a spark is made between the electric wire portion, which has encountered the intermittent short circuit, and the body of the vehicle. As a result, there is apprehension that the electric wire is damaged.